Single-sided four-way indexable positive cutting insert and insert mill therefor

ABSTRACT

A single-sided four-way indexable cutting insert includes a positive basic shape, a rake surface, a peripheral surface including four side abutment surfaces, a base bearing surface and a screw hole connecting the rake and base bearing surfaces. The insert has an imaginary square frustum which defines a square base containing the cutting insert&#39;s base bearing surface, and further defines four isosceles trapezoid side surfaces respectively containing the cutting insert&#39;s four side abutment surfaces. A material volume V F  of the cutting insert and a void volume V S  of the insert fulfill the condition V S /V F ≥0.25.

RELATED APPLICATIONS

This is a Bypass Continuation of PCT/IL2018/051101, filed Oct. 14, 2018and published as WO 2019/106648A1. Priority is claimed to U.S.Provisional Patent Application No. 62/683,268, filed Jun. 11, 2018. Thecontents of the aforementioned applications are incorporated byreference in their entirety.

FIELD OF THE INVENTION

The subject matter of the present invention relates to single-sidedfour-way indexable positive cutting inserts (hereinafter also“insert(s)”) and insert mills therefor. More particularly, to relativelysmall such inserts and tool holders configured for 90° shoulder millingoperations.

BACKGROUND OF THE INVENTION

For the purposes of the present invention, end mills can betheoretically divided into two general groups, namely insert-mills andsolid end mills.

Insert-mills are milling tools which comprise tool holders with pocketsand replaceable inserts, typically indexable, configured to be mountedin the pockets. An advantage of insert-mills is that the replaceableinserts, which are made of comparatively expensive, harder, materialconstitutes a relatively small portion of the milling tool. The toolholders comprise a shank which is held securely by a collet or chuckduring milling.

Unlike insert-mills which regularly require replacement of small insertsand less regularly require replacement of the tool holder, solid endmills comprise integrally formed teeth and the entire solid end mill isreplaced after it is worn. Solid end mills also comprise an integrallyformed shank which is held securely by a collet or chuck during milling.Accordingly, solid end mills utilize far more comparatively expensivematerial than insert-mills. Despite the comparatively higher cost, oneof the advantages of solid end mills over insert-mills is that the solidend mill's single integrally formed body can be manufactured with acomparatively smaller diameter (typically less than 20 mm diameter, withsmaller diameters being more popular, e.g., at about 12 mm diameter)allowing milling in relatively smaller locations than is possible orpractical with insert-mills.

While very small inserts are known, solid end mills are still commonlypreferred at the relatively smaller diameters for a variety of reasons.

Accordingly, the present invention is directed to inserts and insertmills that have a range of design features that make them functionallyand economically competitive with solid end mills at cutting diametersof 20 mm and less, particularly in the range of 9 to 16 mm, preferably 9to 12 mm.

A publication of interest is EP 3050655, which discloses single-sidedtwo-way indexable inserts for small diameter tool holders.

It is an object of the present invention to provide a new and improvedcutting insert and tool holder therefore. Particularly cutting insertsfor small diameter applications and that can be used on a common toolholder. A separate object is provision of an anti-rotation construction.

SUMMARY OF THE INVENTION

The present invention provides a single-sided four-way indexable cuttinginsert for 90° shoulder milling operations for small diameter toolholders. Four indexable positions are typically preferred over the twoindexable positions disclosed in EP 3050655, yet the design chosen in EP3050655 was deliberately chosen to have only two indexable positions,presumably because this was the optimal design conceived by theinventors thereof for small diameter tool holders.

The present invention conceives that even at such small diameters afour-way indexable insert, e.g. of basic square shape, can be provided.Traditionally, during 90° shoulder milling operations for four-wayindexable inserts, two adjacent cutting edges of the insert will be usedsimultaneously, one radially located cutting edge for machininglaterally and another axially located cutting edge for providing a wiperfunction at the axial end of the insert mill. Since the cutting edgeproviding the wiper function already undergoes wear, it was believedthat four indexable positions were not available, and such inserts weredisadvantageous over the elongated two-way indexable type shown in EP3050655, which can provide a longer cutting edge.

It will be noted that cutting inserts having more than four cuttingedges on one side are known, however these inserts are not known forsuch small diameters. This is because, in order to compensate for theabove-mentioned wear on a cutting edge used as a wiper, the cutting edgeis typically not straight but comprises a small wiper portion and alarger relieved cutting edge portion. Thus the overall cutting edgelength of an already small insert is reduced.

Similarly, double sided inserts with even more than four edges areknown, but being able to provide clearance for such cutting inserts inextremely small diameter tool holders is problematic.

Accordingly, it has been found by the present inventor that the wiperfunction has not caused significant wear and a usage of the entirecutting edge, even after it has been used in a wiper position, as a maincutting edge position is possible for small diameter tool holders.

Additionally, a number of advantageous features have been incorporated,each of which is designed to allow economical production in order for aninsert mill of small diameter to be competitive against solid end millsof similar diameter, as will be described below.

According to a first aspect of the present invention there is provided asingle-sided, four-way indexable cutting insert having a positive basicshape and comprising: a rake surface; a base bearing surface locatedopposite the rake surface; an insert axis (A_(I)) extendingperpendicular to the base bearing surface and through the center of theinsert, the insert axis defining: an upward direction from the basebearing surface towards the rake surface, a downward direction oppositeto the upward direction, and an outward direction perpendicular to theupward and downward directions and extending away from the insert axis;a cutting insert height H_(I) measurable parallel to the insert axis,from the base bearing surface to a highest point of the rake surface; aperipheral surface connecting the rake surface and base bearing surface,the peripheral surface comprising: an unground lower sub-surface whichextends upwardly and outwardly from the base bearing surface, the lowersub-surface comprising first, second, third and fourth side abutmentsurfaces; and an upper sub-surface connecting the lower sub-surface andthe rake surface, the upper sub-surface beginning in the upwarddirection at a minimum upper surface height H_(U) above the base bearingsurface; a cutting edge formed along an intersection of the peripheralsurface and rake surface; a screw hole opening out to the rake and basebearing surfaces, the screw hole having a void volume V_(s); wherein:the insert has an imaginary square frustum defined by: a square basecontaining the base bearing surface; four isosceles trapezoid sidesurfaces, each extending upwardly and outwardly from the square base atan abutment surface relief angle θ fulfilling the condition 1°≤θ≤15°,and each containing a respective one of the first, second, third andfourth side abutment surfaces; and a square top connecting the fourisosceles trapezoid side surfaces and located a distance equal to thecutting insert height H_(I) from the square base; the upper sub-surfacecomprises at least one overhanging portion, which extends outwardly froman adjacent one of the trapezoid side surfaces and has a lowermost pointat said minimum upper sub-surface height H_(U); in a view parallel tothe insert axis (A_(I)), an inscribed circle diameter I_(C) of thecutting edges fulfills the condition I_(C)≤10 mm; and a volume ratioV_(S)/V_(F) of the void volume V_(S) and a material volume V_(F) of thecutting insert fulfills the condition V_(S)/V_(F)≥0.25.

In addition to the above-mentioned discovery about the wiper surface, byutilizing a small insert, namely having an inscribed circle diameterI_(C) of less than or equal to 10 mm, it has been found that such smallinserts undergo relatively small distortion (typically a convex bulge)in the sintering process. Such distortion is traditionally dealt with byeither providing a pocket lateral abutment surface with a gap (to ensurethe convex insert side abutment surface securely contacts the lateralabutment surface on both sides of the gap), or by providing apre-designed recess on the side surface of the cutting insert, or byexpensive grinding of the side of the cutting insert.

Since the cutting insert of the present invention is small, thedistortion is within reasonable tolerances and the above-mentionedmodification of the pocket and peripheral grinding of the cutting insertcan be avoided. Thus, the insert is defined as having an unground lowersub-surface. As is known in the art, ground surfaces can be identifiedby grinding lines and discontinuity lines where a planar ground surfaceends and an unground surface starts.

Further, such pocket design is thereby also useful for small four-wayindexable circular-type inserts, which typically cannot be mounted tothe same pocket as they contact the center of the lateral abutmentsurface (and hence would contact a gap in the traditional lateralabutment surface). Further, other types of inserts such as four-wayindexable feed inserts could also be used with such tool holders, makingthe tool holders of the present invention more versatile and hence moreeconomical.

Accordingly, there is an additional advantageous feature of the at leastone overhanging portion, which separates the peripheral portion of theinsert for mounting to the insert pocket (i.e. the lower sub-surface)and the cutting portion of the insert (i.e., the cutting edge). Thus,when producing different cutting edge types (90° or circular, etc.) thesame basic insert, or at least the same pocket, can be used.

Having a positive basic shape, i.e. allowing a pressing process with aslittle machining as possible, as disclosed in EP 3050655B1 (par.[0034]), also contributes to the economic advantage of the presentdesign. It will be noted that the term “positive basic shape” morespecifically means that cross sectional areas nearer to a base bearingsurface of the insert are smaller than cross sectional areas furtheraway therefrom, but does not require all the peripheral surfaces to becontinuously slanted. For example, at certain sections of the insert thesurfaces may extend parallel with an insert axis.

Finally, the amount of material of the insert itself can be minimized.It has been found that the volume ratio V_(S)/V_(F) defined above hasperformed successfully. Naturally, minimizing the amount of material andproviding four indexable positions can provide an economic advantage.

While each of the four main design features mentioned above (namely,four indexable positions, unground lower sub-surface due to small size,at least one overhanging portion, and volume minimizing material) areeach individually advantageous the combination of all four elements inthe present aspect is believed to provide a cutting insert with multipleadvantages.

Additionally, while the intended use of the main insert of the presentinvention is 90° shoulder milling operations, such inserts are extremelysmall and versatile and hence could be used for other operations such aschamfering (by rotating a pocket orientation) or drilling, etc.

According to a second aspect of the present invention there is providedan insert mill comprising: a tool holder; and a cutting insert accordingto the previous aspect.

In such an insert mill, the tool holder can comprise: a shank portion; acutting portion connected to the shank portion and comprising a pocket;and a rotation axis extending through the center of the tool holder anddefining a forward direction extending from the shank portion in thedirection of the cutting portion; with the pocket comprising: a seatabutment surface; a threaded pocket hole opening out to the seatabutment surface and defining a minimal pocket hole inscribed circleI_(P) and an associated minimal pocket hole diameter D_(P); and firstand second lateral abutment surfaces oriented at a right angle to eachother in a plan view of the seat abutment surface; and wherein: each ofthe first and second lateral abutment surfaces has an elongatedcontinuous shape, the first and second lateral abutment surfaces beingthe only abutment surfaces of the pocket apart from the seat abutmentsurface; and the cutting insert is mounted to the pocket with theinsert's base bearing surface abutting the pocket's seat abutmentsurface and two of the insert's adjacent side abutment surfaces abuttingthe pocket's first and second lateral abutment surfaces.

It should be noted that the above defined “right angle” is not meant tomean exactly 90° but rather within manufacturing tolerances, i.e. about90°±3°, preferably 90°±1°.

As mentioned above, a four-way indexable insert with an unground lowersub-surface and a pocket as defined above allows simple production ofthe pocket and versatility in that the pocket can also accommodate evenother types of four-way indexable inserts.

According to a third aspect of the present invention there is provided atool holder as defined in the second aspect.

According to a fourth aspect of the present invention there is provideda four-way indexable cutting insert having a circular cutting edge andexactly four equally spaced side abutment surfaces.

According to a fifth aspect of the present invention there is provided afour-way indexable cutting insert having a volume ratio ofV_(S)/V_(F)≥0.30.

It will be understood that a greater volume ratio utilizes lessmaterial. Accordingly it is preferred that the volume ratio fulfills thecondition: V_(S)/V_(F)≥0.30, or even V_(S)/V_(F)≥0.35. An approximatedmaximum volume ratio for acceptable modern cutting conditions is,theoretically, believed to fulfill the condition: V_(S)/V_(F)≤0.55. Thismaximum volume ratio is particularly relevant to a circular-type insertwhich has extremely little material according to the present invention.With regard to square edged inserts, an approximated maximum volumeratio of V_(S)/V_(F)≤0.40 is likely the approximate maximum volumeratio.

It will be understood that even though the inscribed circle diameterI_(C) defined above allows the lower sub-surface to be unground, evensmaller sizes will allow smaller diameter tool holders to be used and/orto have additional inserts. Accordingly it is preferred that theinscribed circle diameter I_(C) fulfills the condition: I_(C)≤8 mm, oreven I_(C)≤6.5 mm, and most preferably I_(C)≤5 mm. An approximatedminimum feasible size is believed to fulfill the condition: I_(C)≥3.5mm.

It will be understood that a larger minimum upper sub-surface heightH_(U) allows a greater height of the lower sub-surface. The lowersub-surface provides a bearing function and hence a maximized heightthereof provides greater stability to the insert when mounted in thepocket. Conversely, sufficient size of the upper sub-surface is neededfor the cutting function. Accordingly, it is preferred that the minimumupper sub-surface height H_(U) fulfills the condition: 0.60H_(I)≤H_(U)≤0.90 H_(I), or even 0.60 H_(I)≤H_(U)≤0.80 H_(I), and mostpreferably 0.63 H_(I)≤H_(U)≤0.73 H_(I).

The at least one overhanging portion can be a single continuousoverhanging portion extending along the entire periphery of the insertor can be a plurality of circumferentially spaced apart overhangingportions, as is preferred in some embodiments, such as the circular edgeinsert, as explained below.

The cutting insert can preferably be 90° rotationally symmetric aboutthe insert axis. Stated differently, the cutting insert can have fouridentical sides.

The cutting insert can comprise four identical corners and fouridentical straight edges connecting the corners. It will be understoodthat this provides a simple economic shape, free of complex geometries.Stated differently, the insert can have a basic square shaped edge withround corners. This shape can be the most preferred shape which has longstraight edges for cutting.

According to one preferred example each straight edge has an edge lengthL_(E) which fulfills the condition: 0.65 I_(C)<L_(E)<0.95I_(C).Preferably, the edge length L_(E) fulfills the condition: 0.75I_(C)<L_(E)<0.90I_(C). Thus, for an extremely small insert the entirestraight edge on one side of the insert can serve as a main cuttingedge, and the entire straight edge on an adjacent side can serve as awiper. Notably, since the insert is so small, the entire edgeconstitutes a relatively large wiper (raising the concern above of wearwhen used as a wiper). In many known designs this is overcome by anon-straight edge, i.e. a small wiper adjacent to a corner followed by arelieved edge portion following a different direction. In the presentinvention, however, each straight edge can have a simpler geometry,serving as a larger wiper when in one indexed position, and thenfunctioning as a main cutting edge after indexing of the insert.Notably, a large wiper can provide better finish on a machinedworkpiece.

Alternatively, the basic insert shape can have a very small straightedge and a very large corner radius for other than 90° shoulder millingoperations (resembling a circular insert's operation). In such anembodiment, the edge length L_(E) fulfills the condition: 0.10I_(C)<L_(E)<0.50I_(C), preferably 0.15 I_(C)<L_(E)<0.35I_(C).

Still alternatively, the cutting edge can be, for example circular.

Most preferably, the base bearing surface is ground. In a most preferredembodiment, only the base bearing surface of the cutting insert isground. This is the most economical production of the insert.

In some applications, it is necessary to carry out an additional rakesurface grinding operation. In such an embodiment, the base bearingsurface and the entire cutting edge are ground and the cutting edge iscontained within the square top. Stated differently, the grindingoperation is not conducted on the entire peripheral surface, but merelyalong the top of the insert and therefore the entire edge is containedwithin a plane, in this case described as being contained within thesquare top. It will be understood that such top grinding of the insertallows a multitude of inserts to be ground in a single pass. While thisis disadvantageous in some respects, it can be offset by the pocketbeing inclined to provide a suitable positive cutting position.

For some applications, it is also possible to produce a cutting edgecontained within the square top within desired tolerances and withoutsuch a grinding operation, which is of course preferred as it is moreeconomical.

For greater stability, the abutment surface relief angle θ preferablyfulfills the condition 2°≤θ≤8°, and most preferably 4°≤θ≤7°.

In order to provide suitable performance, a cutting edge land widthW_(L) measurable perpendicular to the insert axis taken at any positionalong the cutting edge fulfills the condition: W_(L)≤0.14 mm. Preferablythe land width W_(L) fulfills the condition: 0.02 mm≤W_(L)≤0.14 mm, oreven more preferably 0.03 mm≤W_(L)≤0.11 mm, and most preferably 0.04mm≤W_(L)≤0.08 mm.

The pocket is preferably slanted with respect to the rotation axis ofthe tool holder to compensate for a cutting edge being planar, i.e.contained in the top square.

The pocket hole can similarly be comparatively large in cross sectioncompared with the distance to the lateral abutment surfaces. This can beseen from a pocket hole diameter and distances to the lateral surfaces.

The lateral surfaces are preferably typically oriented at the same angleas the insert's abutment surfaces.

The screw axis can preferably be offset from the center of the seatabutment surface, i.e., slightly more proximate to where the lateralsurfaces are closest to each other, so that a screw holding the cuttinginsert to the pocket will bias the cutting insert towards the lateralsurfaces.

The most advantageous application for an insert in accordance with thepresent invention is believed to be insert mills for cutting smalldiameters, particularly for the standard diameter ranges of 9.7 mm to 16mm. Even though an insert mill of the standard diameter size of 6 mmwith a single cutting insert, and insert mills of even larger diametersare possible, it is believed that they are less efficient than othertool holders at those sizes. For the small size insert exemplified(I_(C)=4 mm), insert mills at 9.7 mm diameter having two inserts, at 12mm diameter having two or even three inserts, at 14 mm diameter havingfour inserts and at 16 mm diameter having five inserts are feasible. Itwill be noted that the present invention is most advantageous at thelower end of the diameter range mentioned, particularly 9.7 mm and 12 mminsert mills. The benefit of which can be noted by multiplying thenumber of inserts mentioned by four (i.e. the number of indexablepositions available for each insert).

According to a sixth aspect there is provided a cutting insertcomprising a rake surface, a generally planar base bearing surface, aperipheral surface connecting the rake surface and base bearing surface,a screw hole having a central axis, and a cutting edge formed at anintersection of the peripheral surface and rake surface; the insertbeing indexable about the central axis; the peripheral surfacecomprising a first side abutment surface, a first non-abutment surfaceadjacent to a first side abutment surface, a second side abutmentsurface, a second non-abutment surface adjacent to a second sideabutment surface; the first side abutment surface and first sidenon-abutment surface being located between adjacently located first andsecond corners; the second side abutment surface and second sidenon-abutment surface being located between said second corner and athird corner adjacent to the second corner; the first and second sidenon-abutment surfaces each being spaced further from the central axisthan the first and second side abutment surfaces.

As will be clear from the description below, not only the present aspectbut any of the previous insert aspects could also comprise the featuredescribed in the sixth aspect or as described in FIGS. 15 to 18B below(stated differently, the feature is, in summary, a pair of adjacent sideabutment surfaces and side non-abutment surfaces, each side non-abutmentsurface being spaced further from a central axis than each side abutmentsurface). The advantage of which is particularly notable when portionsof a cutting edge between two adjacent corners have different geometries(i.e. different cutting functions).

For example, the feature, when, for example, defining for a four-wayindexable insert could be defined as: the peripheral surface furthercomprises a first side non-abutment surface adjacent to the first sideabutment surface, a second side non-abutment surface adjacent to thesecond side abutment surface, a third side non-abutment surface adjacentto the third side abutment surface and a fourth side non-abutmentsurface adjacent to the fourth side abutment surface; wherein each ofthe first, second, third and fourth non-abutment surfaces are spacedfurther from the central axis than the first, second, third and fourthabutment surfaces.

Stated differently, a first length L1 can be measureable from a centralaxis A_(I) to each side abutment surface 38′, and a second length L2 canbe measureable from the central axis A_(I) to each side non-abutmentsurface 39′; and the first length L1 is smaller than the second lengthL2. In mathematical terms such relationship can be expressed as: L2=L1+Δ(where Δ is the difference between the first length L1 and second lengthL2). The second length L2 can preferably be defined with the followingcondition: 0.04 mm<Δ<0.5 mm, more preferably 0.06 mm<Δ<0.2 mm, and mostpreferably 0.06 mm<Δ<0.1 mm.

Preferably, the insert is a four-way indexable cutting insert.Preferably, the cutting edges are identical for each indexed position.

Preferably, the insert is a feed insert with adjacent ramp and feedcutting edges between two adjacent corners. Preferably, each sidenon-abutment surface is generally located under the feed cutting edgeand each side abutment surface is generally located under the rampcutting edge.

Preferably, the adjacent side non-abutment surfaces are oriented at thesame angle as the pocket's first and second lateral abutment surfaces.

Preferably, the adjacent side non-abutment surfaces are oriented at thesame index angle as the side abutment surfaces.

Preferably, in a cross sectional view perpendicular to a central axis, awidth of the side abutment surface is greater than a width of the sidenon-abutment surface.

Preferably, the peripheral surface comprises a relief sub-surfaceadjacent to the base bearing surface. To elaborate, the reliefsub-surface is more inwardly located than the surface above it. Mostpreferably, the relief sub-surface is located underneath the sidenon-abutment surface. Additionally, it is preferable the reliefsub-surface can also be located underneath the side abutment surface.Most preferably, the relief sub-surface can be located underneath boththe side abutment surface and the side non-abutment surface. In the mostpreferred embodiment, the relief sub-surface can extend around theentire insert peripheral surface. Preferably, the relief sub-surface isconvexly curved.

Preferably, the rake surface can comprise a negative land.

Preferably the rake surface can comprise a convexly curved rake surfaceportion adjacent to the ramp cutting edge.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the subject matter of the presentinvention, and to show how the same may be carried out in practice,reference will now be made to the accompanying drawings derived from ascale model, in which:

FIG. 1A is a side view of an insert mill comprising a tool holder and aplurality of inserts according to the subject matter of the presentinvention, rotated to show a front (i.e., axial) view of the leftmostinsert;

FIG. 1B is a side view of the insert mill in FIG. 1A, rotated to show aside view of the leftmost insert in FIG. 1A;

FIG. 1C is an end view of the insert mill in FIGS. 1A and 1B;

FIG. 2 is an end view of an insert mill, similar to the insert millshown in FIGS. 1A to 1C, except with two inserts;

FIG. 3 is an end view of an insert mill, similar to the insert millshown in FIGS. 1A to 1C, except with five inserts;

FIG. 4 is a perspective view of the leftmost insert shown in FIG. 1A;

FIG. 5A is a cross-section view taken along line VA-VA in FIG. 6C;

FIG. 5B is a cross-section view taken along line VB-VB in FIG. 6C;

FIG. 5C is a cross-section view taken along line VC-VC in FIG. 6C;

FIG. 6A is a side view of the insert in FIG. 4;

FIG. 6B is a cross-section view taken along line VIB-VIB in FIG. 6A;

FIG. 6C is a top (i.e. axial) view of the insert in FIG. 6A;

FIG. 7A is a top view of an imaginary square frustum, showing the squaretop thereof;

FIG. 7B is a side view of the square frustum in FIG. 7A, showing anisosceles trapezoid side surface thereof;

FIG. 7C is a bottom view of the square frustum in FIG. 7A, showing thefour isosceles trapezoid side surfaces thereof and the square basethereof;

FIG. 7D is another side view of the square frustum in FIG. 7A, rotated;

FIG. 7E is a schematic side view of the insert in FIG. 4, shown withinthe square frustum;

FIG. 7F is a perspective view of the square frustum in FIG. 7A;

FIG. 7G is a schematic perspective view of the insert in FIG. 4, shownwithin a portion of the square frustum and hatching schematicallyindicating where the trapezoid side surfaces of the square frustumcontain the side abutment surfaces of the cutting insert;

FIG. 8A is a perspective view of a pocket of any one of the insert millsin FIGS. 1A to 3;

FIG. 8B is a side view of the pocket in FIG. 8A;

FIG. 8C is a top (i.e. axial) view of the pocket in FIG. 8A, and alsoconstitutes a plan view of the seat abutment surface of the pocket;

FIG. 9 is a perspective view of another insert and hatchingschematically indicating where the trapezoid side surfaces of a squarefrustum (not shown) would contain the side abutment surfaces of thecutting insert;

FIG. 10A is a cross-section view taken along line XA-XA in FIG. 11C;

FIG. 10B is a cross-section view taken along line XB-XB in FIG. 11C;

FIG. 11A is a side view of the insert in FIG. 9;

FIG. 11B is a cross-section view taken along line XIB-XIB in FIG. 11A;

FIG. 11C is a top (i.e. axial) view of the insert in FIG. 11A;

FIG. 11D is a cross-section view taken along line XID-XID in FIG. 11A;

FIG. 12 is a perspective view of another insert and hatchingschematically indicating where the trapezoid side surfaces of a squarefrustum (not shown) would contain the side abutment surfaces of thecutting insert;

FIG. 13A is a cross-section view taken along line XIIIA-XIIIA in FIG.14C;

FIG. 13B is a cross-section view taken along line XIIIB-XIIIB in FIG.14C;

FIG. 13C is a cross-section view taken along line XIIIC-XIIIC in FIG.14C;

FIG. 14A is a side view of the insert in FIG. 12;

FIG. 14B is a cross-section view taken along line XIVB-XIVB in FIG. 14A;

FIG. 14C is a top (i.e. axial) view of the insert in FIG. 14A;

FIG. 14D is a cross-section view taken along line XIVD-XIVD in FIG. 14A;

FIG. 15 is a perspective view of another insert and hatchingschematically indicating where the trapezoid side surfaces of a squarefrustum (not shown) would contain the side abutment surfaces of thecutting insert;

FIG. 16A is a cross-section view taken along line XVIA-XVIA in FIG. 17C;

FIG. 16B is a cross-section view taken along line XVIB-XVIB in FIG. 17C;

FIG. 16C is a cross-section view taken along line XVIC-XVIC in FIG. 17C;

FIG. 17A is a side view of the insert in FIG. 15;

FIG. 17B is a cross-section view taken along line XIIVB-XIIVB in FIG.17A;

FIG. 17C is a top (i.e. axial) view of the insert in FIG. 17A; and

FIG. 17D is a cross-section view taken along line XIIVD-XIIVD in FIG.17A;

FIG. 18A is a top view of a pocket corresponding to the pocket in FIGS.8A to 8C comprising an insert according to FIGS. 15 to 17D but onlyshowing a cross section view corresponding to FIG. 17D, the insert beingin a correct mounting position; and

FIG. 18B is a similar view to FIG. 18A except that the insert is shownin an incorrect mounting position.

DETAILED DESCRIPTION

FIGS. 1A to 1C illustrates an insert mill 10 configured for 90° shouldermilling operations.

The insert mill 10 comprises a tool holder 12, cutting inserts 14 andscrews 16 for securing the cutting inserts 14 to the tool holder 12.

The insert mill 10 is configured for rotating about a rotation axisA_(R) which extends longitudinally through the center thereof.

The rotation axis A_(R) defines opposite axially forward and rearwarddirections D_(F), D_(R), and opposite rotational cutting and non-cuttingdirections D_(C), D_(N).

The tool holder 12 comprises a shank portion 18 and a cutting portion 20extending forward therefrom.

The cutting portion 20 comprises one or more pockets 22.

In the example shown in FIGS. 1A-1C, there are three pockets 22 (shownwithout inserts in FIGS. 8A to 8C). For smaller diameter tool holders itis only possible to provide less pockets, for example a two pocketembodiment of an insert mill 10′ is shown in FIG. 2. For larger diametertool holders more pockets may be provided as shown in the tool holder10″ in FIG. 3.

The cutting inserts 14, screws 16 and pockets 22, in the examples given,are identical, therefore features described with respect to one shouldbe considered to apply to all.

The cutting insert 14 will now be described with reference to FIGS.4-6C.

The cutting insert 14 is a single-sided four-way indexable cuttinginsert having a positive basic shape. It comprises a rake surface 24, agenerally planar base bearing surface 26, a peripheral surface 28, ascrew hole 30, and a cutting edge 32.

An insert axis A_(I) (FIG. 6A) extends perpendicular to the base bearingsurface 26 and through the center of the insert 14. The insert axisA_(I) is provided to assist defining directions and features of thecutting insert 14. Generally speaking, while it is most preferred that ascrew hole of the present invention is located in the center of aninsert and is perpendicular to a base bearing surface, resulting in aninsert axis of the insert also extending through the center the screwhole, it will be understood that it is possible a screw hole can beslanted or not perfectly central to a cutting insert, resulting in ascrew hole axis (not shown) which is not coaxial with the insert axisA_(I) (whereas in the present preferred example they are coaxial).Nonetheless, given that the present invention seeks to minimize materialusage to the greatest extent possible, certainly for the purposes ofstructural strength the exemplified central and perpendicular screw holeis preferred.

The insert axis A_(I) defines opposite upward and downward directionsD_(U), D_(D), and opposite inward and outward directions D_(I), D_(O).The outward direction D_(O) is not meant to define one specificdirection but rather all possible 360° outward directions from theinsert axis A_(I), three such directions being exemplified. This is alsotrue, in the opposite direction, for the inward direction D_(I).

As shown, for example in FIGS. 4 and 5C, the rake surface 24 canpreferably slope inwardly and downwardly from the cutting edge to forman acute internal angle α for chip forming purposes.

The base bearing surface 26 is generally planar as shown, but it will beunderstood that this definition does not preclude the possible inclusionof a small rounded transition edge between the peripheral surface andthe base bearing surface, as shown for example in FIG. 7 of EP 3050655.

Referring to FIGS. 4 and 6A, the peripheral surface 28 comprises a lowersub-surface 34 and an upper sub-surface 36. The lower sub-surface 34 isunground and extends upwardly and outwardly from the base bearingsurface 26, and comprises first, second, third and fourth side abutmentsurfaces 38A, 38B, 38C, 38D. (In FIG. 4 only 38A and 38B are shown andthe positions of 38C and 38D, which are hidden, are schematicallyidentified; hereinafter the identical side abutment surfaces will beidentified generally as “side abutment surface(s) 38”).

Referring to FIGS. 6A and 6B, the positive basic shape of the cuttinginsert 14 means that the lower sub-surface 34 forms an obtuse internalangle β₁ with the base bearing surface 26. Preferably, althoughoptionally, the upper sub-surface 36 forms an obtuse internal angle β₂with the base bearing surface 26. Alternatively, it is possible for theupper sub-surface 36 to be, for example, perpendicular to the basebearing surface 26.

Each of the side abutment surfaces 38 is generally planar. To elaborate,an exaggerated schematic convex bulge 40 is shown in FIG. 6C. The bulge40 typically results from a sintering process. Since the inserts of thepresent invention are small, distortion resulting in such bulge 40 isacceptably small enough for them not to require grinding. Generallyspeaking, such convexity or concavity (not shown; which can beconsidered an inward “bulge” for the purposes of the specification) ismeasured as a maximum distance from a plane connecting adjacent cornersof an insert to such bulge.

Thus, the insert is stated to have unground lower sub-surface. Eventhough in FIG. 4, for example, it appears to have a discontinuity line42, this is merely a result of this particular drawing showing acurvature line. An actual product which has not been ground does nothave a discernable line, and smoothly transitions from the generallyplanar portion to the radius.

The upper sub-surface 36 comprises at least one overhanging portion 44,described below further in reference to FIGS. 7A to 7G.

Referring to FIG. 6C, the cutting insert 14 can comprise four identicalcorners 46A, 46B, 46C, 46D (hereinafter generally referred to as“corner(s) 46”) and four identical straight edges 48A, 48B, 48C, 48D(hereinafter generally referred to as “straight edge(s) 48”) connectingthe corners.

Dimensions of various features are shown as follows: each corner canhave a radius R (FIG. 6C); each straight edge 48 can have an edge lengthL_(E) measured from the transition point of the radius of the corners(FIG. 6C); a cutting edge land width W_(L) is shown in FIG. 5B; and animaginary inscribed circle C, and a diameter I_(C) thereof is shown inFIG. 6C.

Referring to FIGS. 6B and 6C, a void volume V_(S) of the cutting insert14 is defined by the boundaries of the screw hole 30. Specifically, ascrew hole height Hs is defined from the base bearing surface 26 to anupper edge 49 of the screw hole 30 (also designated in FIG. 4). Stateddifferently, the void volume V_(S) is calculated as the volume of thevoid extending from a bottom of the screw hole 30, defined at a lowerplane P_(L) perpendicular to the insert axis A_(I) and essentiallycoplanar with the base bearing surface 26, to a top of the screw hole 30defined at an upper plane P_(T) perpendicular to the intersection of thescrew hole 30 and the rake surface 24, i.e. at the height of the upperedge 49. More precisely, as shown in FIG. 5A, the upper edge 49 is anintersection of a curved corner 51 of the screw hole 30 and the rakesurface 24.

The material volume V_(F) is, as its name states, the volume of theactual material of which the cutting insert 14 is made.

Referring now to FIGS. 7A to 7G, an imaginary square frustum 50 is showncomprising a square base 52, four identical isosceles trapezoid sidesurfaces 54A, 54B, 54C, 54D (noting that in FIG. 7F only 54A and 54B areshown and the positions of 54C and 54D, which are hidden, areschematically identified; hereinafter generally referred to as“trapezoid side surface(s) 54”) and a square top 56 which is larger thanthe square base 52.

Each trapezoid side surface 54 extends upwardly and outwardly from thesquare base 52 (or, equivalently, downwardly and inwardly from thesquare top 56) at an abutment surface relief angle θ fulfilling thecondition 1°≤θ≤15° (FIG. 7D).

The hatching, schematically designated as 58A, 58B in FIG. 7G (notingthat not the entire height of the square frustum is shown) schematicallyshows where the first and second side abutment surfaces 38A, 38B arerespectively contained within the isosceles trapezoid side surfaces.

Similarly, the square base 52 contains the base bearing surface 26.

As, in this example, the cutting edge 32 is located at a single height,i.e. a cutting insert height H_(I) from the square base 52, the squaretop 56 contains the cutting edge 32.

FIG. 7E shows, in a side view, where the at least one overhangingportion 44 extends further outward from the isosceles trapezoid sidesurfaces 54. In this example, there is only a single overhanging portion44, continuously extending around the entire periphery of the insert.

The upper sub-surface 36 (FIG. 6A) begins, in the upward direction, at aminimum upper sub-surface height H_(U) above the base bearing surface26, the minimum upper sub-surface height H_(U) being measurable parallelto the insert axis A_(I). The at least one overhanging portion 44 has alowermost point 60 at the minimum upper sub-surface height H_(U) abovethe base bearing surface 26.

Referring now to FIGS. 8A to 8C, the pocket 22 comprises a seat abutmentsurface 62, a threaded pocket hole 64 opening out to the seat abutmentsurface 62 and defining a minimal pocket hole inscribed circle I_(P) andan associated minimal pocket hole diameter D_(P), first and secondlateral abutment surfaces 66A, 66B oriented at a right angle to eachother in a plan view (i.e. the view in FIG. 8C) of the seat abutmentsurface 62.

The pocket hole 64 can similarly be comparatively large in cross sectioncompared with the distance to the lateral abutment surfaces. This can beseen from the pocket hole diameter D_(P) and the distances from thepocket hole 64 to the lateral abutment surfaces 66A, 66B.

The first and second lateral surfaces 66A, 66B are preferably typicallyoriented at the same obtuse internal angle β₁ as the insert's abutmentsurfaces 38.

A screw axis As can preferably be offset from a center of the seatabutment surface, i.e. slightly more proximate to where the lateralsurfaces are closest to each other (i.e. the area generally designated68) so that a screw holding the cutting insert to the pocket will biasthe cutting insert towards the lateral surfaces.

Referring now to FIGS. 1A to 1C, a tool recess 70 is preferably providedso that a tool can easily access a screw 16 mounted to the pocket 22.

When mounted, the screw 16 secures the cutting insert 14 such that thebase bearing surface 26 abuts the seat abutment surface 62, the firstabutment surface 38A abuts the first lateral surface 66A, and anadjacent abutment surface 66 (in this example the fourth abutmentsurface 38D, shown in FIG. 1C) abuts the second lateral surface 66B. Itwill be understood that the cutting insert 14 can be indexed four timesin the pocket 22 and that the exact designation of which specificabutment surfaces contact at any given time is not important.

More importantly, it is noted that the upper sub-surface 36 does notcontact the tool holder 12 and therefore inserts with different cuttingedges can be mounted on the same tool holder 12.

The pocket is preferably slanted in the forward direction D_(F) andcutting direction D_(C) with respect to the rotation axis A_(R), asshown by a slant angle μ. The slant angle μ can preferably fulfill thecondition 2°≤μ≤5°.

In FIG. 1B, for the insert mill 10 exemplified, one of the straightcutting edges (for example the third straight edge 48C) performs a wiperfunction and only protrudes a small wiper distance D_(W) from the toolholder. Notably the orientation thereof is at a right angle to therotation axis A_(R). In this example, the second straight edge 48B isthe main cutting edge for providing a 90° shoulder milling operation.

Referring to FIG. 1A, since the entire cutting edge 48 (exemplified asthe second straight edge 48B) is straight and generally parallel to therotation axis A_(R), a comparatively large cut depth A_(P) is achievablefor a comparatively very small cutting insert. For the same reason, thisis similarly true that the entire third straight edge 48C provides acomparatively large wiper, generally perpendicular to the rotation axisA_(R).

Referring now to FIGS. 9 to 11D, a different insert embodiment, i.e., acircular insert 14′, is shown. The pocket's first and second lateralabutment surfaces 66A, 66B have no gap in the center thereof, as istypically provided to counter an insert bulge described above. Becausethe pocket's first and second lateral abutment surfaces 66A, 66B aredevoid of a gap, a circular insert such as the cutting insert designated14′, which will abut the center portions of the first and second lateralabutment surfaces 66A, 66B can be used in the exact same pocket 22 asthe previously described insert 14.

The circular insert 14′ is a single-sided four-way indexable cuttinginsert having a positive basic shape. Apart from the shapes of thecutting edge 32′, side abutment surfaces 38′ and overhanging portions44′, the circular insert 14′ can be considered to be otherwise similarto the previously described insert 14. Accordingly, only significantdifferences will be detailed.

Reference numerals corresponding to those used in the previouslydescribed insert, but suffixed with an apostrophe (′) should beconsidered to have comparative function.

The cutting edge 32′ is completely circular and hence also correspondsto the imaginary inscribed circle C′.

The side abutment surfaces 38′ can preferably but optionally taper inthe downward direction D_(D) (FIG. 11A). Stated differently, they canhave a frustum shape (noting that it is not a triangular shape since theoverhanging portion is not included as part of the side abutmentsurface).

While the tapering shape extends from the cutting edge 32′ to the basebearing surface 26′, it will be understood that the abutment of the sideabutment surfaces 38′ and the pocket's lateral abutment surfaces willonly be with the hatched portions, two of which are shown in FIG. 9.

Finally, it will be noted that at least one overhanging portion 44′ isactually four spaced-apart, separate overhanging portions. As shown inFIG. 10B, in contrast to FIG. 10A, certain circumferential portions ofthe peripheral surface 28′ are devoid of any overhanging portion 44′.FIG. 10A is view through a cross section through the center of the sideabutment surface 38′ as understood from FIGS. 11C and 11D. By having aplurality of spaced-apart overhanging portions, both a fully circularcutting edge can be achieved while still having four generally planarside abutment surfaces vertically separated from the cutting edge forproviding four distinct indexing positions.

Referring now to FIGS. 12 to 14D, a different insert embodiment, i.e. afeed insert 14″, is shown.

The feed insert 14″ is similar to the previous inserts in most respectsexcept that the cutting edge has been designed for feed milling (i.e.comprising combined ramping and feed machining capability. Accordingly,only significant differences will be detailed.

Reference numerals corresponding to those used in the previouslydescribed insert, but suffixed with two apostrophes (″) should beconsidered to have comparative function.

The feed insert 14″ merely exemplifies that the side abutment surfaces38″ can be located in a position other than the center of the sidesurface of the insert. Stated differently, they can be generally planaronly adjacent to corners of the insert. The hatched portions of the sideabutment surfaces 38″ in FIG. 12 will similarly be contained within theabove described isosceles trapezoid side surfaces. Thus the same toolholder 12 can also be used to provide a feed function.

Referring now to FIGS. 15 to 17D, a different insert 14′″ is shown.

The feed insert 14′″ is similar to the previous inserts and particularlythe insert designated 14″, since both have a cutting edge has beendesigned for feed milling (i.e. comprising combined adjacent ramping andfeed cutting edges (or sub-edges) adjacent to each other).

Unless specified to the contrary, features with similar referencenumerals are similar or identical to the previous inserts. Significantdifferences are detailed below.

The cutting insert 14′″ is a single-sided four-way indexable cuttinginsert having a positive basic shape. It comprises a rake surface 24′″,a generally planar base bearing surface 26′″, a peripheral surface 28′″,a screw hole 30′″, and a cutting edge 32′″.

An insert axis A_(I) (FIG. 6A) extends perpendicular to the base bearingsurface 26′″ and through the center of the insert 14′″.

Referring to FIG. 17A, it can be seen that the insert's the peripheralsurface 28′″ comprises a lower sub-surface 34′″ and an upper sub-surface36′″.

Directing attention first to the lower sub-surface 34′″, there are fouridentical side abutment surfaces 38′″ corresponding in function to thosedescribed above.

Unlike the previous inserts, portions of the peripheral surface 28′″located adjacent to the side abutment surfaces 38′″ have been designedfor a special function and have consequently been given a name, namelyside non-abutment surfaces 39′″.

More precisely, between each side abutment surface 38′″ and anon-adjacent corner 41′″ of the same side abutment surface there is aside non-abutment surfaces 39′″.

For example, using FIG. 15, additional reference numerals (i.e. inaddition to 38′″ and 39′″) added for explanation only. A first sideabutment surface designated 100 (also generally designated 38′″) islocated between a so-called adjacent corner 102 and a non-adjacentcorner 104. Between the first side abutment surface 100 and thenon-adjacent corner 104 is a so-called non-abutment surface 106 (alsogenerally designated 39′″). Between each pair of adjacent corners thereare corresponding side abutment surfaces and side non-abutment surfaces,however as they are identical they will not be described.

Similar to the previous examples, the hatching shown for each sideabutment surface 38′″ schematically shows where the insert's sideabutment surfaces 38′″ are respectively contained within theabove-described isosceles trapezoid side surfaces, which also abuts atool's pocket when mounted correctly thereto.

As noted above, the pocket of the present invention can accommodatedifferent inserts, and unlike typical prior art design is not configureddifferently for each different type of four-way indexable insert.

During testing, it was unexpectedly found that it was possible to mountthe feed insert 14″ in FIG. 14 incorrectly to the pocket of the presentinvention, i.e. in a rotated position from the correct position. Thisderived from two unusual circumstances.

A first circumstance was that the adjacent non-abutment surfaces locatedbetween the abutment surfaces 38″ were oriented at basically the sameindex angle as the pocket's first and second lateral abutment surfaces66A, 66B (in this example 90°; i.e. which is also the same index angleas the intended adjacent abutment surfaces 38″), which allows anoperator the chance to mistakenly secure the insert using non-abutmentsurfaces.

A second circumstance in which the insert has two different functioningsub-edges adjacent to each other (i.e. between adjacent corners).Accordingly, while such incorrect mounting would not be problematic withan insert having all symmetric edges, in the case of a fast feed insertor other type of insert with non-identical adjacent functioning edges,such incorrect mounting is unacceptable.

To reduce the likelihood, and preferably eliminate, said incorrectmounting the side non-abutment surfaces 39′″ were spaced from thecentral axis A_(I) of the insert 14′″ a greater distance than theabutment surfaces 38′″.

To elaborate with an example, referring to FIG. 17D, a first length L1measured from the central axis A_(I) (i.e. the center of the insert) tothe side abutment surface 38′″ (the side abutment surface exemplified isalso designated 100) is smaller than a second length L2 measured fromthe central axis A_(I) (i.e. the center of the insert) to the adjacentside non-abutment surface 39′″ (also designated 106). In mathematicalterms such relationship can be expressed as: L2=L1+Δ(where Δ is thedifference).

Notably, from the drawing it is hard to see the length difference as itis very small. In the given example L1=1.9 mm and L2=1.98 mm. Notingthat an inscribed circle of the insert 14′″ measuring within the sideabutment surfaces 38′″ is consequently twice the magnitude of L1, i.e.3.8 mm (i.e. 3.8 mm is an inscribed diameter of the abutment surfaces38′″).

Stated differently, the exemplified above mentioned difference Δ is 0.08mm or approximately 2% of an inscribed diameter of the abutmentsurfaces. A minimum working value of the difference Δ is estimated to beabout 0.04 mm (i.e. below which the desired effect preventing incorrectmounting may not be effective) and a maximum working value is estimatedto be about 0.5 mm. Consequently, a second length L2 from the centralaxis A_(I) to a non-abutment surface is preferably 0.04 mm<Δ<0.5 mm,more preferably 0.06 mm<Δ<0.2 mm, and most preferably 0.06 mm<Δ<0.1 mm

Referring now to FIGS. 18A and 18B, the effect of the above feature isshown in a pocket 22 and is identical with that previously described.

To reiterate the relevant features for this example, the pocket 22comprises a threaded pocket hole 64, first and second lateral abutmentsurfaces 66A, 66B and a screw axis As extending through the center ofthe threaded pocket hole 64.

In the correct mounted position in FIG. 18A, two adjacent the sideabutment surfaces 38′″ abut the first and second lateral abutmentsurfaces 66A, 66B and as a result the insert's central axis A_(I) andthe pocket hole's screw axis As are spaced a relatively small thirdlength L3 from each other. Accordingly, a screw (not shown) can beinserted through the insert's screw hole 30′″ and the pocket hole 64 tosecure the insert 14′″ to the pocket 22.

By contrast, in the incorrect mounted position in FIG. 18B, adjacentside non-abutment surfaces 39′″ abut the first and second lateralabutment surfaces 66A, 66B and as a result the insert's central axisA_(I) and the pocket hole's screw axis A_(S) are spaced a relativelylarger fourth length L4 from each other (i.e. fourth length L4 beingrelatively larger than length L3). Accordingly, a screw (not shown) isimpeded from being inserted through the insert's screw hole 30′″ duepart of the edge 108 of the pocket hole 64 protruding in it's path.

It has been observed that the non-abutment surfaces 39′″ can cause theinsert 14′″ to automatically adjust or rotate into the correct mountedposition as shown in FIG. 18A when an operator is securing the insert14′″ to the pocket hole 64.

The present embodiment is a fast feed insert, however due to theinteresting discovery of having two different possible abutment surfaces(i.e. an abutment surface adjacent to a non-abutment surface, both ofwhich being possibly used for mounting an insert to a pocket), it isnoted that such feature (increasing the length of one of the abutmentsurfaces to greater than the other to prevent incorrect mounting) couldalso be reversed. This could be, for example if the cutting edge wouldnot be configured as a fast feed cutting edge but if, for example, theadjacent corner edges of the insert could be functional to provide atypical milling insert.

Stated differently, referring to FIG. 15, for a fast feed insert (notnecessarily the exemplified fast feed insert 14′″ being used forexplanatory purposes only), the non-abutment surfaces (39′″, 106; beingpositioned further from the central axis A_(I) than the intendedabutment surfaces) are positioned below the main cutting edges 110 andnot below the ramping edges 112, and the abutment surfaces (38′″, 100)are positioned below the ramp cutting edges 112.

As shown in FIG. 17D, a first width W1 of the side abutment surface isgreater than a second width W2 of the side non-abutment surface. It willbe understood that this was a preferred but non-limiting way to push theside non-abutment surface 39′″ further from the central axis A_(I). Itwill be understood that such modification also affects the connectedside abutment surface 38′″.

While the main concept of the present example has been described above,which in itself is even a separate patentable aspect, some preferredfeatures for such concept are as follows.

As a result of the side non-abutment surfaces 39′″ being spaced furtherthan the side abutment surface 38′″ from the central axis A_(I), theinsert peripheral surface 28′″ is further formed with a reliefsub-surface 114 adjacent to the base bearing surface 26′″.

The relief sub-surface 114 has been included since, during translationalmotion of the insert 14′″ during milling, there is increased likelihoodof the insert peripheral surface 28′″ undesirably contacting a workpiece(not shown).

A more important addition of the relief sub-surface 114 is underneaththe non-abutment surface 39′″ (designated 114A) which is most likely tocontact a workpiece (not shown) as it protrudes further from the centerof the insert 14′″. However there is also increased likelihood that thearea underneath the abutment surface 38′″ may contact a workpiece andhence said relief sub-surface 114 is also added underneath the insertabutment surface 38′″ (designated 114B). For ease of production therelief sub-surface 114 extends around the entire insert peripheralsurface 28′″.

Notably, adding said relief sub-surface 114 under the insert abutmentsurface 38′″ is somewhat disadvantageous since it reduces stability (dueto a smaller abutment area), but is believed to be overall beneficial.Accordingly, such addition of the relief sub-surface 114 along anyportion of the insert peripheral surface 28′″ is a preferred butnon-limiting option.

In this preferred but non-limiting example the relief sub-surface 114 isconvexly curved.

Another preferred but optional feature, shown best in FIG. 16A, is aneutral or even negative land 116. As described above, it is preferablethat a rake surface slope inwardly and downwardly from the cutting edgeto form an acute internal angle α for chip forming purposes. However,similar to that stated above, as a result of the increased likelihood ofcontact with a workpiece due to the non-abutment surface being outwardlyspaced, it is preferred to reinforce the cutting edge, even at thedetriment caused to cutting efficiency. Such reinforcement even is addedin the form of a convexly curved rake surface portion 116 adjacent tothe ramp cutting edge 112.

What is claimed is:
 1. A single-sided, four-way indexable cutting inserthaving a positive basic shape and comprising: a rake surface; a basebearing surface located opposite the rake surface; an insert axis AIextending perpendicular to the base bearing surface and through a centerof the insert, the insert axis defining: an upward direction from thebase bearing surface towards the rake surface, a downward directionopposite to the upward direction, and an outward direction perpendicularto the upward and downward directions and extending away from the insertaxis; a cutting insert height HI measurable parallel to the insert axis,from the base bearing surface to a highest point of the rake surface; aperipheral surface connecting the rake surface and base bearing surface,the peripheral surface comprising: an unground lower sub-surface whichextends upwardly and outwardly from the base bearing surface, the lowersub-surface comprising first, second, third and fourth side abutmentsurfaces; and an upper sub-surface connecting the lower sub-surface andthe rake surface, the upper sub-surface beginning in the upwarddirection at a minimum upper surface height HU above the base bearingsurface; a cutting edge formed along an intersection of the peripheralsurface and rake surface; and a screw hole opening out to the rake andbase bearing surfaces, the screw hole having a void volume V_(S);wherein: the insert has an imaginary square frustum defined by: a squarebase containing the base bearing surface; four isosceles trapezoid sidesurfaces, each extending upwardly and outwardly from the square base atan abutment surface relief angle θ fulfilling the condition 1°≤θ≤15°,and each containing a respective one of the first, second, third andfourth side abutment surfaces; and a square top connecting the fourisosceles trapezoid side surfaces and located a distance equal to thecutting insert height HI from the square base; the upper sub-surfacecomprises at least one overhanging portion, which extends outwardly froman adjacent one of the trapezoid side surfaces and has a lowermost pointat said minimum upper sub-surface height HU; in a view parallel to theinsert axis AI, an inscribed circle diameter IC of the cutting edgesfulfills the condition IC≤10 mm; a volume ratio VS/VF of the void volumeVS and a material volume VF of the cutting insert fulfills the conditionVS/VF≥0.25; and the peripheral surface further comprises a first sidenon-abutment surface adjacent to the first side abutment surface, asecond side non-abutment surface adjacent to the second side abutmentsurface, a third side non-abutment surface adjacent to the third sideabutment surface and a fourth side non-abutment surface adjacent to thefourth side abutment surface; wherein each of the first, second, thirdand fourth non-abutment surfaces are spaced further from the centralaxis than the first, second, third and fourth abutment surfaces.
 2. Thecutting insert according to claim 1, wherein the volume ratio fulfillsthe condition: 0.30≤VS/VF≤0.60.
 3. The cutting insert according to claim1, wherein the inscribed circle diameter IC fulfills the condition: 3.5mm≤IC≤6.5 mm.
 4. The cutting insert according to claim 3, wherein theinscribed circle diameter IC fulfills the condition: 3.5 mm≤IC≤5 mm. 5.The cutting insert according to claim 1, wherein the minimum uppersub-surface height HU fulfills the condition: 0.60HI≤HU≤0.90HI.
 6. Thecutting insert according to claim 1, wherein the at least oneoverhanging portion is a plurality of overhanging portions.
 7. Thecutting insert according to claim 1, wherein the cutting edge comprisesfour identical corners and four identical straight edges connecting thecorners.
 8. The cutting insert according to claim 7, wherein eachstraight edge has an edge length LE which fulfills the condition:0.65IC<LE<0.95lC.
 9. The cutting insert according to claim 1, whereinonly the base bearing surface of the cutting insert is ground.
 10. Thecutting insert according to claim 1, wherein the base bearing surfaceand the entire cutting edge are ground and the cutting edge is containedwithin the square top.
 11. The cutting insert according to claim 1,wherein the cutting edge is circular.
 12. The cutting insert accordingto claim 1, wherein a first length L1 is measureable from the centralaxis AI to each side abutment surface, and a second length L2 ismeasureable from the central axis AI to the each side non-abutmentsurface; the first length L1 being smaller than the second length L2 anda difference Δ between them fulfills the condition: L2=L1+Δ.
 13. Thecutting insert according to claim 12, wherein the difference Δ fulfillsthe condition: 0.04 mm<Δ<0.5 mm.
 14. The cutting insert according toclaim 1, wherein the insert is a feed insert with adjacent ramp and feedcutting edges between each pair of adjacent corners.
 15. The cuttinginsert according to claim 14, wherein each non-abutment surface isgenerally located under one of the feed cutting edges and the abutmentsurface is generally located under one of the ramp cutting edges. 16.The cutting insert according to claim 14, wherein the peripheral surfacecomprises a relief sub-surface adjacent to the base bearing surface. 17.The cutting insert according to claim 16, wherein the relief sub-surfaceis convexly curved.
 18. The cutting insert according to claim 1, whereinthe rake surface comprises a negative land.
 19. The cutting insertaccording to claim 1, wherein the rake surface comprises a convexlycurved rake surface portion adjacent to a ramp cutting edge.
 20. Thecutting insert according to claim 1, wherein a first width W1 of eachside abutment surface is greater than a second width W2 of the eachnon-abutment surface.
 21. An insert mill comprising: a tool holder; anda cutting insert according to claim 1, seated in the tool holder;wherein: the tool holder comprises: a shank portion; a cutting portionconnected to the shank portion and comprising a pocket; and a rotationaxis extending through the center of the tool holder and defining aforward direction extending from the shank portion in the direction ofthe cutting portion; the pocket comprises: a seat abutment surface; athreaded pocket hole opening out to the seat abutment surface anddefining a minimal pocket hole inscribed circle IP and an associatedminimal pocket hole diameter DP; and first and second lateral abutmentsurfaces oriented at a right angle to each other in a plan view of theseat abutment surface; each of the first and second lateral abutmentsurfaces has an elongated continuous shape, the first and second lateralabutment surfaces being the only abutment surfaces of the pocket apartfrom the seat abutment surface; and the cutting insert is mounted to thepocket with the insert's base bearing surface abutting the pocket's seatabutment surface, and two of the insert's adjacent side abutmentsurfaces abutting the pocket's first and second lateral abutmentsurfaces.
 22. The insert mill according to claim 21, wherein: thecutting edge is circular; and the insert's two adjacent side abutmentsurfaces abut center portions of the pocket's first and second lateralabutment surfaces.